1. Field of the Invention
This invention relates, generally, to surge protection devices. More particularly, it relates to a surge protection device that relies on the capacitive properties of MOV as a part of an impedance network for failure identification.
2. Description of the Prior Art
A metal oxide varistor (MOV) is a device that monitors the proper working of a surge protector. Conventional metal oxide varistor (MOV) failure identification technologies rely on thermal fuses. Conventional surge protectors include thermally protected metal oxide varistors (TMOV) and thermally protected varistor series with indicating lead (iTMOV).
There are numerous surge protection devices currently available. However, until recently, there were no means for indicating whether or not the surge protection device was operated properly. Surge protectors that indicate thermal fuse failure only, for example, may not be operating properly due to MOV failure but no indication is provided to the user that the surge protector has failed. Instead, since the thermal fuse is still intact, the user gets a false indication that the surge protector is still working.
Destruction of an MOV will not affect the normal operation of a surge protector because MOVs are shunt elements. Ironically, poorly designed surge protectors give some indication of destruction by appearing singed, whereas well-designed surge protectors do not appear damaged after destruction.
To avoid a fire hazard, thermal protection schemes are used to prevent the MOV from reaching its thermal destructive level. The use of thermal protective fuses allows the use of LEDs indicating protection and fault operation. Also, it is very important that ground and neutral wires are correctly connected. Since MOVs are surge diverters, if the neutral wire is not connected then the destructive energy cannot be diverted away from the sensitive load.
It is possible that after much surge suppression, the thermal limit of the fuse may not be reached, but the MOV may degrade and fail. Conventional surge protectors do not indicate that such a failed MOV is no longer in service. Such conventional surge protectors will indicate failure only if the thermal fuse has failed.
There is a need for a surge protector design that provides more efficient and safer surge protector circuit operations.
There is also a need for a design that indicates normal and failure modes of MOVs. Such a design would not rely on thermal fuses to identify the presence of an MOV.
However, in view of the prior art taken as a whole at the time the present invention was made, it was not obvious to those of ordinary skill how the identified needs could be fulfilled.